The present invention relates generally to dolly wheels for use with a vehicle to provide maneuverability that results in what are termed zero turn capabilities. More specifically, the present invention relates to dolly wheels that have a steering control system that allows dolly wheel type response to steering at low speeds and in conditions where such dolly wheel effect is advantageous and precise directional control steering of the dolly wheels at high speeds and in conditions of variable traction of the vehicle and terrain as is also advantageous.
Dolly wheels are commonly used on vehicles or other devices which operate at low speeds (0 -10 m.p.h.). However, when the speed of the vehicle increases, such as to 15 m.p.h. or greater, current dolly wheels can become unstable and oscillate or shimmy. The oscillation or shimmying is a phenomenon characterized by the vibration or rotation of the dolly wheel about its axis. The oscillation or shimmying is caused in part by offset load impacts on the wheels, such as can occur when the side of the dolly wheel surface that engages the road contacts resistance, stones or bumps, which cause the wheel to rotate and then recenter when the trailing dolly effect again becomes the controlling directional force on the wheel. In rapidly recentering, the wheel typically goes past center and then must recenter back again. The rapid effect of this phenomenon sets up an ongoing shimmy or oscillation which is disruptive to the smooth operation of the vehicle.
As the speed of the vehicle increases, the need for rapid response of the dolly wheels and full rotation of the dolly wheels is lessened. At higher speeds, as discussed, however, road impacts to the dolly wheels can excite oscillation and instability of the dolly wheel axles. It would therefore be desirable to provide a dolly wheel system which resists the dynamic excitation caused by use of the dolly wheels at high speed.
As is known, with dolly wheel steering systems the front wheels follow the vehicle""s motion direction as the vehicle rotation and hence, steering is normally provided by the drive axle. Such a system with drive axle steering utilizes free rotating dolly wheels that are configured to swivel 360 degrees with the trailing wheel center allowing for automatic alignment. In addition to instability at high speeds, this zero turn capability about the driven axis can cause instability when the vehicle encounters rough terrain with the free rotating dolly wheels providing no directional stability, which can result in loss of directional control. For example, because the dolly wheels respond to the unequal speeds of the drive wheels, undesired vehicle rotation and hence turning can result, such as when one drive wheel experiences slippage due to lack of traction or when the vehicle is driving along a side hill where the tires see unequal weight and thus unequal traction, or a side hill where the vehicle weight over the dolly wheel wants to pull that end downhill, whereas a steered tire would hold the desired vehicle path. At slower speeds and in normal conditions, however, the dolly wheels are required to have complete freedom to follow the drive wheel turn requirements.
Presently, various methods and designs have been developed to reduce these problem of shimmying and oscillating. Some of these designs have used hydraulic braking devices and friction devices in order to restrain movement of the dolly wheels regardless of the speed of the vehicle. Moreover, some of these hydraulic brakes operate only at certain positions of the dolly wheels and others operate for the entire 360 degrees of rotation of the dolly wheel axle. They are thus constrained by when they can be deployed. Moreover, these systems only attempt to prevent shimmying at high speeds.
Presently, there are no known systems that provide direct steering control over dolly wheels on a vehicle at any speed. This is because to do so would eliminate benefits that accompany dolly wheel steering. Thus, it would be desirable to provide a dolly wheel system that can be fully controlled without losing the maneuverability provided by dolly wheels.
It is therefore an object of the present invention to provide a dual mode steering system for a dolly wheel that provides varying dampening of the dolly wheel when in the free rotation mode for advantages in reduced shimmy and oscillation and stability in conditions leading to the need for full controlled steering.
It is therefore also an object of the present invention to provide a dual mode steering system for a dolly wheel that provides direct steering control at higher speeds or uneven traction condition for vehicle stability and yet maintains the advantages of free rotating dolly wheel maneuverability at low speeds.
It is another object of the present invention to provide a dual mode steering system for a dolly wheel that restricts the free rotation of the pivot axis in relation to speed or uneven traction of the vehicle employing the dolly wheel when the dolly wheel is to be steered either manually or automatically.
It is a further object of the present invention to provide a dual mode steering system that allows for steering control of a dolly wheel within a certain predetermined steering range and allows for normal dolly wheel operation outside of the predetermined steering range.
It is still another object of the present invention to provide a dual mode steering system that provides for steering control of a dolly wheel upon demand.
It is still another object of the present invention to provide a steering system with the ability to provide complete steering control capability which simulates dolly wheel steering in order to provide the advantages of dolly wheel steering and full control steering.
It is still a further object of the present invention to provide a steering system or dual mode steering that can be incorporated into a mobility vehicle such as, but not limited to a personal mobility vehicle, a utility vehicle, a trailed device or an automobile.
It is yet another object of the present invention to provide a dual mode steering system that allows a steering control over dolly wheel when a vehicle is being parked, when a vehicle is being maneuvered on a hillside or tight locations, and when a vehicle is operated in conditions of lessened steering control due to drive wheel slippage.
In accordance with the above and the other objects of the present invention, a dual mode dolly wheel steering system is provided. The dolly wheel system includes a dolly wheel, a dolly wheel spindle assembly in communication with the dolly wheel, such that the dolly wheel and the dolly wheel spindle are fixedly secured to one another and are rotatable as a single unit. The dolly wheel spindle is in communication with a dampening and/or coupling device and a steering control system. The steering control system and the dampening device are each in communication with a controller to regulate actuation of each. When a signal from the controller requests utilization of steering control, the dampening and/or coupling device applies a restraining force to the dolly wheel spindle to limit rotation of the dolly wheel. When the rotation of the dolly wheel spindle is restrained relative to the steering control system, the steering control system can effectuate direct steering control of the dolly wheels to provide precise directional control. It is understood that dolly wheel position sensors that detect the position of the wheel relative to the vehicle axis of travel and the orientation requested by the steering input can define movement of the dolly wheel to effectuate desired controlled steering. Conversely, when the control indicates that the normal dolly wheel capability is desired, the restraining force applied to the dolly wheel spindle by the dampening device is relieved and the steering control system is overridden. By the then free relationship of the dolly wheel to the steering control system, a level of dampening may be maintained to resist shimmy and oscillation.
The dampening device may be comprised of an electroviscous fluid in combination with the corresponding contours of the spindle shaft and surrounding chamber, which is in communication with the controller to result in a varying resistance to restrict motion of the dolly wheel.
The dampening device may be comprised of an electric motor, a hydraulic pump/motor, or a mechanical dxc3xa9tente system each of which is in communication with the controller to result in a resistance to restrict motion of the dolly wheel.
The steering control system may be comprised of a hydraulic, electric, pneumatic, or mechanical powered steering input which is in communication with the controller to provide the ability for corrective steering when demanded or for corrective steering in the forward speed vehicle operation.
Other objects and features of the present invention will become apparent when viewed in light of the detailed description of the preferred embodiment when taken in conjunction with the attached drawings and appended claims.